The present invention relates to a device for joining by elastic tightening. More specifically, the invention relates to the joining by means of a tight device of two parts comprising tightening means of the screw-nut type which move the parts to be joined towards one another in order to compress a gasket between these parts.
In such a device, the tightening means can in particular be constituted by bolts or two ring-shaped parts cooperating by means of a thread, depending on whether the parts to be joined have a large or small diameter. Generally, existing joining devices are assembled by operating the tightening means in accordance with a tightening range adapted to the mechanical characteristics of the gasket used. For this purpose, either a manual torque wrench or a preset, semi-automatic mechanical spanner is used. The final tightening torque is usually obtained after the spanner has carried out a number of turns of each bolt. During this operation, the tensile stresses in the bolts balance the compressive stresses in the flanges.
This widely used method is economic, but is also irksome and relatively inaccurate, because a large proportion of the forces used serve to overcome friction beneath the head and at the threads. When the use conditions impose a precise tightening or when the consequences of jamming of the nuts and bolts may be serious, it is necessary to employ more sophisticated methods.